WO2017116275A1

WO2017116275A1 - Method of pig iron production using romelt liquid phase reduction process

Info

Publication number: WO2017116275A1
Application number: PCT/RU2016/000194
Authority: WO
Inventors: Vladimir Andreevich Romenets; Valery Sergeevich Valavin; Yury Valentinovich POKHVISNEV; Sergey Aleksandrovich MAKEEV; Aleksander Konstantinovich ZAYTSEV; Nataliya Vyacheslavovna SIMAKOVA; Alena Aleksandrovna FEDOROVA
Original assignee: Moskovsky Institut Stali I Splavov
Current assignee: Moskovsky Institut Stali I Splavov
Priority date: 2015-12-29
Filing date: 2016-04-06
Publication date: 2017-07-06
Anticipated expiration: 2018-06-29
Also published as: EA201800393A1; EP3397779A1; EP3397779A4; KR20180097739A; EA033747B1; RU2618297C1

Abstract

The invention relates to the pig iron production in the Romelt furnace. Simultaneous loading of iron containing materials, fluxes and >5 mm sized coal fractions into the liquid slag bath of the Romelt furnace through the top loading port. Bubbling of the liquid slag bath and initiation of coal combustion by supplying air/oxygen blowing gas to the bottom tuyeres. Oxidation of released CO and H₂ by supplying oxygen to the top tuyeres. The combustion rate of the gases is maintained at 60-85% of the maximum possible rate by dividing coal into >5 mm and <5 mm fractions. The <5 mm coal fraction is crushed to <1 mm size and supplied to the liquid slag bath through the bottom tuyeres together with the air/oxygen blowing gas at a rate of 400-1000 m³ /m²of furnace area at the bottom tuyere level. A heat flow of 3-6 MW/m² of liquid slag bath area is provided from the combustion zone to the liquid slag bath. The invention provides reduction of iron loss with the slag and exclusion of uncontrolled boiling of a slag bath.

Description

Method of Pig Iron Production using Romelt Liquid Phase Reduction

Process

Field of the Invention. This invention relates to ferrous metallurgy, more specifically, to the production of liquid carbon-bearing semiproduct and pig iron; furthermore, it can be used in other branches of industry, for example, in non-ferrous metallurgy, production of construction materials etc.

Prior Art. Known is the Romelt pig iron production process by liquid phase reduction that comprises continuous loading into the same slag bath iron- containing materials of different mineral composition, all coal and lime, supply of oxygen, oxygen blowing to the zones above and below the slag level and the output of the product metal, slag and gases (V.A. Romenets et al., Romelt Process, Moscow, MISiS, Ore and Metals, 2005, p. 8).

Disadvantage of this method is its limited controllability only based on the coal and oxygen consumption calculated using material balance equations, whereas melting occurs regardless of the coal particle size distribution. All coal is supplied through the loading ports in the top of the furnace to the slag bath. Practical experiments show that for the Romelt process the combustion rate calculated on the basis of the composition of the carbon-containing output gases C0₂/(C0₂+CO) does not exceed 0.3-0.5 while the theoretical rate is close to 1. Romelt furnace operation with low combustion rates causes a significant growth in power consumption and reduces process output. Furthermore, the quantity of heat supplied to the slag bath and the intensity of blowing through the bottom tuyeres cannot be controlled.

The closest counterpart of the present invention is the Romelt Process Control Method (RU 2182603, published 20.05.2000 ) according to which the content of iron oxides in the slag is controlled and maintained at the required level depending on slag temperature and gas composition by increasing or decreasing the quantity of loaded coal and increasing or decreasing the quantity of oxygen supplied to above the molten slag level.

According to that method, process control and pig iron production are also achieved regardless of the coal particle size distribution, all coal being loaded from the top of the furnace. The method does not either provide for high gas combustion rates.

Disadvantage of these methods is that for top coal loading into the slag bath, 3-5 mm sized coal particles do not reach the slag bath or are carried away from it without having interacted with iron oxides. These particles circulate in the post-combustion zone and interact with C0₂ and H₂0 forming during combustion to reduce the combustion rate and heat transfer to the bath. The combustion rate does not exceed 0.3-0.5, and oxygen and carbon are over- consumed.

The above processes do not allow one take into account or control the heat flow from the combustion zone to the slag bath which should be optimized and maintained within certain limits. This factor is critical in the design of Romelt furnaces because its disregard may yield incorrect results.

Disclosure of the Invention. The technical result achieved using this invention is as follows:

- possibility of Romelt furnace operation with high combustion rates and efficient use of fine coal fractions without compromise to melting results;

- possibility of efficient use of fine coal fractions due to their blowing into the slag bath in the vicinity of the bottom tuyeres;

- reduction of iron loss with slag to below 5% compared with melting of highly oxidized materials using the classical Romelt process due to an increased iron oxide reduction rate;

- avoiding uncontrolled boiling of the slag bath; - controlling and maintaining at the optimum level of unit oxygen consumption for the bottom tuyeres.

The above technical result is achieved as follows.

For the Romelt liquid phase reduction process, iron containing materials, fluxes and >5 mm sized coal fractions are simultaneously loaded into the Romelt furnace liquid slag bath through the top loading port. The bottom slag bath is bubbled and initial coal burning are achieved by supplying the air/oxygen blowing mixture to the bottom tuyeres of the Romelt furnace. CO and H₂ released from the liquid slag bath are oxidized in the combustion zone by supplying oxygen to the top tuyeres of the Romelt furnace. The combustion rate of the gases released from the liquid slag bath is maintained at 60-85% of the maximum possible combustion rate by dividing coal into >5 and <5 mm sized fractions.

<5 mm sized coal fractions are crushed to <1 mm size and supplied to the liquid slag bath through the bottom tuyeres of the Romelt furnace together with oxygen at a rate of 400 - 1000 m³/m² of furnace area at the bottom tuyere level. The heat flow from the combustion zone to the liquid slag bath is maintained at 3-6 MW/m of liquid slag bath area.

Said iron containing materials are metallurgical waste such as slams, dust, scale and iron ores.

Furthermore, said fluxes can be lime or fired dolomite or quartz sand or mixtures thereof.

The combustion rate of the gases released from the liquid slag bath is calculated based on the ratio of carbon containing components a = CO₂/(CO₂+CO)- 100% where C0₂ and CO are volume percentages of the respective gases after combustion.

The butt and side walls of the Romelt furnace may be fitted with additional and bottom tuyeres. The quantity of <1 mm sized coal fraction supplied to said additional and bottom tuyeres is less than 20% of the overall coal load.

The invention is exemplified a Figure 1 showing an embodiment of the method. Figure 1 shows intermediate gate 1 , single-mesh drum 2, coal loading chutes 3 and 4, first vertical conveyor 5, <1 mm coal crusher 6, second vertical conveyor 7, >5 mm coal fraction charge hopper 8, <5 mm coal fraction charge hopper 9, liquid slag bath 10, top tuyeres 1 1 , bottom tuyeres 12 and top loading port 13.

For the known Romelt process, part of fine coal particles loaded through the top loading port due to the small relative density of coal circulate in the combustion zone above the slag bath, part of them being carried away from the furnace as dust. This is caused by the large gas flows consisting of bath-released gases and blow gases supplied to the top tuyeres. By way of example one can present a calculation of gas flow rate above the slag bath of a test Romelt furnace. For a furnace area of 20 m² at the bottom tuyere level, gas release from the slag bath reached 40-60 ths. m³/h. Thus, taking into account the high temperature of the gases one can asses the linear rate of the upcoming gas flows at 5.4 m/s.

Coal dust interacts with the gas phase to reduce combustion rate. This interaction also affects heat release from the combustion process because incomplete combustion and oxygen shortage only provide for coal combustion to CO, the heat efficiency of this reaction being 117 kJ/mole which is less than half of the CO and H₂ combustion reaction heat efficiencies that are 279 and 251 kJ/mole, respectively.

The coal dust contamination of the gas not only increases the content of CO but also redistributes oxygen between the carbon and hydrogen containing components of the gaseous phase.

The above disadvantages are eliminated in the method provided herein. Embodiments of the Invention. The following embodiment of the method is suggested.

Iron containing materials, fluxes and >5 mm sized coal fractions are simultaneously loaded into the Romelt furnace liquid slag bath 10 through the top loading port 13. Said iron containing materials are wastes of metallurgical production such as slams, dust, scale and iron ores. Said fluxes can be lime or fired dolomite or quartz sand or mixtures thereof.

Simultaneously with the loading of iron containing materials, fluxes and coal, air/oxygen blowing gas is supplied to the bottom tuyeres 12 to initiate coal combustion and bubbling of the liquid slag bath 10.

CO and H₂ released from the liquid slag bath 10 are oxidized in the combustion zone by supplying min. 80% purity oxygen to the top tuyeres 11 of the Romelt furnace.

All the main endothermic reduction reactions of iron oxides and other metal oxides occur in the slag bath of the Romelt process:

(Me_xO_y) + yC = xMe + yCO

The only exothermic reaction of incomplete carbon combustion

C + l/20₂ = CO

does not compensate for heat deficiency, and therefore the overall heat balance of the bath is negative. Complete coal combustion to C0₂ in the slag bath according to the reaction

C + o₂ = co₂

is impossible because this will not provide for the thermodynamic conditions as are required for iron oxide reduction.

For pig iron production from wet iron containing material with the overall iron content Fe_ov = 50% using 65% C_fix thermal coal, the average heat consumption is approx. 12.3 MJ/kg iron taking into account ambience heat loss, whereas the coal combustion reaction releases max. 3 MJ/kg iron which is insufficient for compensating the heat deficiency.

Therefore the main heat source of the Romelt furnace is combustion of the reducing gases above the slag bath with the transfer of the released heat to the bath. The volume of the CO and H₂ gases released from the bath is greater than the one required for compensating the heat deficiency in the slag bath, and therefore even partial combustion of these gases provides for the required heat. For a correctly arranged combustion zone, combustion of 60-85% of the gases released from the bath is sufficient. Combustion heat can be increased by removing the circulating coal particles and hence redistributing all oxygen supplied above the slag level to the gas combustion reaction, as suggested in this invention.

Coal is loaded through the gate 1 to the single-mesh drum 2 which divides it into >5 mm and <5 mm fractions. The larger sized coal fraction (>5 mm) is supplied through the second vertical conveyor 7 to the charge hopper 8 and further to the liquid slag bath 10 through the top loading port 13.

The <5 mm coal fraction is supplied through the loading chute 3 to the first vertical conveyor 5 and further to the charge hopper 9. Then the <5 mm coal fraction is supplied from the charge hopper 9 to the coal crusher 6 where it is crushed to <1 mm particles.

This latter fraction is blown into the liquid slag bath 10 through the bottom tuyeres or through the additional tuyeres provided in the butt and side walls of the Romelt furnace at a 0.8-1.8 m height from the furnace floor.

For a blowing flowrate of less than 400 m /m of furnace area, bubbling in the liquid slag bath does not provide for sufficient melt agitation.

For a blowing flowrate of more than 1000 m /m of furnace area, gas jets may penetrate through the slag bath thus reducing agitation intensity. Iron oxides ending up in the coal containing bubbling slag layer are solved in the slag and reduced by coal particles mixed with the slag. Iron obtained after reduction is enriched in carbon, and its drops deposit by gravity to the furnace floor. Thus, three molten layers form in the furnace: the metal on the furnace floor, the unagitated slag layer between the metal and the bottom tuyeres and the bubbled slag layer (the reaction zone). The blowing in of fine coal fractions increases the quantity of iron reduction centers thus increasing the quality of the output metal and the overall output of the plant.

If coal is divided into >5 mm and <5 mm fractions, the combustion rate of the gases released from the liquid slag bath 10 is maintained at 60-85% of the maximum possible combustion rate.

Coal division into >5 mm and <5 mm fractions is necessitated by the fact that if coal is loaded through the top loading port the >5 mm fraction achieves the slag bath while the <5 mm fraction due to their relatively small density and high gas flow rates circulate in the combustion zone and interact with the oxygen blown to the top tuyeres.

If the combustion rate of the gases released from the liquid slag bath CO₂/(CO₂+CO)- 100% is less than 60% the output of the Romelt furnace decreases and power consumption increases.

If the combustion rate of the gases released from the liquid slag bath is greater than 85%, the forming C0₂ and H₂0 may dissociate due to the high temperature thus increasing the quantity of heat released by combustion and heat loss through the furnace walls.

If the gas combustion rate is considered insufficient, <5 mm coal fraction is supplied using the intermediate gate 1 through the loading chute 4 to the vertical conveyor 5 and the coal crusher 6 for crushing to <1 mm size coal particles. The supply of <1 mm coal fractions is necessitated by the following. If >1 mm sized coal fractions are supplied to the bottom tuyeres 12, the inner surfaces of the coal preparation and supply systems undergo intense mechanical wear due to the exposure of the system surfaces to the sharp coal particles, and the reduction rate in the slag layer decreases.

The quantity of the <1 mm coal fractions supplied to the additional tuyeres and the bottom tuyeres 12 is at least 20% of the overall coal load. At smaller fine fraction percentages the increase in the combustion rate is insufficient for achieving a >60% combustion rate, and the quantity of metallic phase formation centers also increases insufficiently.

Under these conditions, a heat flow of 3-6 MW/m² of liquid slag bath area is provided from the combustion zone to the liquid slag bath. For a heat flow of less than 3 MW/m² of liquid slag bath area, the heat transfer from the combustion zone to the liquid slag bath is insufficient, and there is coal and oxygen overconsumption at the bottom tuyere row. For a heat flow of greater than 6 MW/m of liquid slag bath area, the combustion rate increases, C0₂ and H₂0 dissociation occurs and heat load to the furnace walls increases.

The oxygen consumption at the top tuyeres reduces by 10 m³, the content of the <5 mm coal fraction in the combustion zone decreases by 1 kg of fixed carbon in the coal. In the meantime, the pig iron output of the Romelt furnace will reach 1.2 kg per 1 kg blown-in carbon due to an increase in the iron oxide reduction centers at coal particles.

Examples of method embodiments can be as follows.

Example 1.

The liquid slag bath of the Romelt furnace is simultaneously loaded with a mixture of iron containing metallurgical waste (slams, dust, scale) with the average content Fe_ov = 50.4% and TSSh grade coal of the Kuznetsk coal basin with a fixed carbon content of 67.5%. The >5 mm coal fraction is supplied to the liquid slag bath of the Romelt furnace through the top loading port, and the <5 mm coal fraction is crushed to <1 mm size. Then the <1 mm coal fraction is blown into the liquid slag bath through the bottom tuyeres and through the additional tuyeres provided in the butt and side walls of the Romelt furnace together with the air/oxygen blowing gas at a rate of 1000 m /m of furnace area at the bottom tuyere level. The combustion rate of the gases released from the slag bath is 60% of the maximum possible rate. This provides for a heat flow heat flow of 3 MW/m of liquid slag bath area from the combustion zone to the liquid slag bath. The quantity of the <1 mm coal fraction supplied to the bottom tuyeres is 20% of the overall coal load. The unit coal and oxygen consumptions are 820 kg t iron and 940 m³/t iron, respectively. The output of the furnace is therefore 15% higher compared with the process in which all coal is loaded through the top loading port.

Example 2.

The liquid slag bath of the Romelt furnace is simultaneously loaded with iron ore of average content Fe_ov = 38.5% and T grade coal of the Kuznetsk coal basin with a fixed carbon content of 76.5%. The >5 mm coal fraction is supplied to the liquid slag bath of the Romelt furnace through the top loading port, and the <5 mm coal fraction is crushed to <1 mm size. Then the <1 mm coal fraction is blown into the liquid slag bath through the bottom tuyeres and through the additional tuyeres provided in the butt and side walls of the Romelt furnace together with the air/oxygen blowing gas at a rate of 400 m³/m² of furnace area at the bottom tuyere level. The combustion rate of the gases released from the slag bath is 85% of the maximum possible rate. This provides for a heat flow heat flow of 6 MW/m of liquid slag bath area from the combustion zone to the liquid slag bath. The quantity of the <1 mm coal fraction supplied to the bottom tuyeres is 40% of the overall coal load. The unit coal and oxygen consumptions are 980 kg/t iron and 1030 m /t iron, respectively. The output of the furnace is therefore 30% higher compared with the process in which all coal is loaded through the top loading port.

Thus, the suggested method increases the output of the process and provides for coal and oxygen saving compared with the process in which all coal is loaded through the top loading port into the liquid slag bath.

Claims

What is claimed is a

1. Pig iron production method by the Romelt liquid phase reduction process comprising simultaneous loading of iron containing materials, fluxes and >5 mm sized coal fractions into the liquid slag bath of the Romelt furnace through the top loading port, bubbling of the liquid slag bath and initiation of coal combustion by supplying air/oxygen blowing gas to the bottom tuyeres of the Romelt furnace, oxidation of CO and H₂ released from the liquid slag bath in the combustion zone by supplying oxygen to the top tuyeres of the Romelt furnace and pig iron and slag removal from the Romelt furnace wherein the combustion rate of the gases released from the liquid slag bath is maintained at 60-85% of the maximum possible rate by dividing coal into >5 mm and <5 mm fractions further wherein the <5 mm coal fraction is crushed to <1 mm size and supplied to the liquid slag bath through the bottom tuyeres of the Romelt furnace together with the air/oxygen blowing gas at a rate of 400-1000 m³/m² of furnace area at the bottom tuyere level, and a heat flow of 3-6 MW/m² of liquid slag bath area is provided from the combustion zone to the liquid slag bath.

2. Method of Claim 1 wherein said iron containing materials are metallurgical waste such as slams, dust, scale and iron ores.

3. Method of Claim 1 wherein said fluxes are lime or fired dolomite or quartz sand or mixtures thereof.

4. Method of Claim 1 wherein the combustion rate of the gases released from the liquid slag bath is calculated based on the ratio of carbon containing components a = CO₂/(CO₂+CO) 100%.

5. Method of Claim 1 wherein the butt and side walls of the Romelt furnace are fitted with additional bottom tuyeres. 6 Method of Claim 1 wherein the quantity of <1 mm sized coal fraction supplied to said additional and bottom tuyeres is not less than 20% of the overall coal load.